Moving a thread to a linked environment was reachable only through the
t3_thread_handoff MCP tool. Users now pick "Continue on…" from the web
sidebar and chat-header thread menus, the command palette, and mobile's
long-press and thread header menus. Targets are read from
threadHandoff.options when the menu opens.

The thread shows the move's state above the composer: waiting for the
turn to end (with Keep it here), under way, moved (with Open on <machine>),
or failed. While the thread is departing or departed, the composer is
closed on both clients.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>